The present invention concerns flow controls. They can be inserted in a liquid-supply line or in the accommodating bore of a plumbing fitting. They have an essentially cup-shaped mount with perforations through its bottom. A disk of resilient material fits into the perforations.
Flow controls of this type are preferably employed in the fittings and other components of drinking fountains and are in themselves known. When subjected to pressure by a fluid, the resilient disk constricts the perforations such that the volume of flow remains constant over a specified range of pressure differences.
The resulting volumetric flow and its constancy subject to different pressures extensively depends on the shape and dimensions of the resilient disk. Since resilient materials have wide tolerances in such conditions, the ideal volumetric flow cannot be attained and will not remain constant over extensive ranges of pressure difference.
The initial slope of the controls' characteristic curve depends in particular on the shape of the disk. That shape determines at what minimal pressure difference the controls will attain their rated value. Conventional controls often have a slope that is not as steep as desired and only arrive at their nominal volumetric flow at greater pressure differences.
It has also often been observed that flow controls react dynamically to changes in pressure difference rather slowly, exhibiting considerably hysteresis in response to alternately increasing and decreasing pressure. Furthermore, lasting deformations sometimes occur in the disk and will lead over time to alterations in the characteristic curve.